验证 net.ipv4.tcp_syn_retries:
node2:/root/test#sysctl -p |grep -i syn
error: "net.bridge.bridge-nf-call-ip6tables" is an unknown key
error: "net.bridge.bridge-nf-call-iptables" is an unknown key
error: "net.bridge.bridge-nf-call-arptables" is an unknown key
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_syn_retries = 5
node2:/root/test#iptables -I INPUT -s 192.168.137.2 -j DROP
node2:/root#tcpdump -S -i eth1 '((tcp) and (port 8080) and (host 192.168.137.2) )'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
20:33:02.518794 IP node2.26725 > node1.webcache: Flags [S], seq 2505003061, win 14600, options [mss 1460,sackOK,TS val 137281597 ecr 0,nop,wscale 6], length 0
20:33:02.519175 IP node1.webcache > node2.26725: Flags [S.], seq 1839543175, ack 2505003062, win 1448, options [mss 1460,sackOK,TS val 5535778 ecr 137281597,nop,wscale 6], length 0
20:33:03.517060 IP node2.26725 > node1.webcache: Flags [S], seq 2505003061, win 14600, options [mss 1460,sackOK,TS val 137282597 ecr 0,nop,wscale 6], length 0
20:33:03.517327 IP node1.webcache > node2.26725: Flags [S.], seq 1839543175, ack 2505003062, win 1448, options [mss 1460,sackOK,TS val 5536776 ecr 137281597,nop,wscale 6], length 0
20:33:03.520434 IP node1.webcache > node2.26725: Flags [S.], seq 1839543175, ack 2505003062, win 1448, options [mss 1460,sackOK,TS val 5536778 ecr 137281597,nop,wscale 6], length 0
20:33:05.517568 IP node2.26725 > node1.webcache: Flags [S], seq 2505003061, win 14600, options [mss 1460,sackOK,TS val 137284597 ecr 0,nop,wscale 6], length 0
20:33:05.517928 IP node1.webcache > node2.26725: Flags [S.], seq 1839543175, ack 2505003062, win 1448, options [mss 1460,sackOK,TS val 5538777 ecr 137281597,nop,wscale 6], length 0
20:33:05.521450 IP node1.webcache > node2.26725: Flags [S.], seq 1839543175, ack 2505003062, win 1448, options [mss 1460,sackOK,TS val 5538781 ecr 137281597,nop,wscale 6], length 0
20:33:09.517951 IP node2.26725 > node1.webcache: Flags [S], seq 2505003061, win 14600, options [mss 1460,sackOK,TS val 137288598 ecr 0,nop,wscale 6], length 0
20:33:09.518228 IP node1.webcache > node2.26725: Flags [S.], seq 1839543175, ack 2505003062, win 1448, options [mss 1460,sackOK,TS val 5542777 ecr 137281597,nop,wscale 6], length 0
20:33:09.931628 IP node1.webcache > node2.26725: Flags [S.], seq 1839543175, ack 2505003062, win 1448, options [mss 1460,sackOK,TS val 5543191 ecr 137281597,nop,wscale 6], length 0
20:33:17.517996 IP node2.26725 > node1.webcache: Flags [S], seq 2505003061, win 14600, options [mss 1460,sackOK,TS val 137296598 ecr 0,nop,wscale 6], length 0
20:33:17.518297 IP node1.webcache > node2.26725: Flags [S.], seq 1839543175, ack 2505003062, win 1448, options [mss 1460,sackOK,TS val 5550777 ecr 137281597,nop,wscale 6], length 0
20:33:17.965498 IP node1.webcache > node2.26725: Flags [S.], seq 1839543175, ack 2505003062, win 1448, options [mss 1460,sackOK,TS val 5551225 ecr 137281597,nop,wscale 6], length 0
20:33:33.518823 IP node2.26725 > node1.webcache: Flags [S], seq 2505003061, win 14600, options [mss 1460,sackOK,TS val 137312599 ecr 0,nop,wscale 6], length 0
20:33:33.519357 IP node1.webcache > node2.26725: Flags [S.], seq 1839543175, ack 2505003062, win 1448, options [mss 1460,sackOK,TS val 5566778 ecr 137281597,nop,wscale 6], length 0
20:33:33.995707 IP node1.webcache > node2.26725: Flags [S.], seq 1839543175, ack 2505003062, win 1448, options [mss 1460,sackOK,TS val 5567255 ecr 137281597,nop,wscale 6], length 0
重发了5次 发sync报文的重试次数